Horticulture: Development of Fusarium wilt resistance in celery and understanding of pathogen virulence factors to underpin UK and EU biosecurity

尖孢镰刀菌（Fusarium oxysporum，Fo）真菌物种复合体包括超过100种不同的致病性特化型（formae speciales，f. spp.）适应特定的宿主，包括重要的作物，如芹菜，生菜，西红柿和香草，如香菜。Fo病原体继续在全球范围内传播，其中一些病原体导致重大流行病，最值得注意的是Fo f.sp. cubense导致香蕉上的巴拿马病。Fo病原体的影响往往是巨大的，完全作物损失并不罕见，这已经加剧了缺乏生物安全措施和缺乏远见，在新的Fo f. spp之前开发和部署植物抗性。以及来自其他地区的种族芹菜枯萎病（Fusarium wilt）是影响芹菜生产的重要病害。感染通过根部发生，并由土壤中长寿命的孢子引发。植物的维管系统被侵入，导致发育迟缓、黄化和枯萎。Foa的控制非常具有挑战性，因为杀真菌剂和轮作无效，损失很高;因此，植物抗性的发展是一个优先事项。然而，像其他一些Fo f. spp一样，新的福阿种族已经进化出了克服阻力的能力。Foa存在四个小种，最近出现的小种4在商业芹菜中没有抗性的情况下是最具破坏性的。此外，与其他Foa种族不同，Foa 4也会导致香菜疾病。因此，迫切需要在芹菜中开发对这种疾病的高水平抗性，并评估对英国香菜的影响。目前，Foa主要影响美国和中国的芹菜生产，但病原体传播到欧洲主要作物和种子生产地区（如西班牙，意大利和英国）的风险非常高，这些地区的条件已经适合，但随着气候变化将变得更加有利。芹菜是世界范围内的主要作物，是健康饮食的重要组成部分，因为它富含纤维，矿物质和维生素。芹菜的最大生产国是美国和西班牙，但英国也有大量生产。值得注意的是，总部位于英国的GS种植者是欧洲最大的芹菜生产商，他们在西班牙种植的大部分作物全年供应。该作物对项目合作伙伴Tozer Seeds也至关重要，因为他们是全球主要的芹菜育种者和种子供应商之一。因此，保护欧洲和英国的芹菜作物免受Foa 4的未来到来是非常重要的。该项目的主要目的是通过在Tozer Seeds的各种芹菜类型中鉴定对Foa 4的新抗性来源来应对枯萎病的挑战。此外，我们还将评估选定的商业香菜品系对病原体的反应。由于芹菜多样性集的基因组刚刚被测序，我们还将确定与这种抗性相关的基因组部分和基因序列变异，以开发DNA标记。这可以大大加快培育新品种的速度，因为抗性很容易通过DNA分析确定，而不需要进行植物试验。最后，我们还将对来自不同种族的Foa分离物以及来自香菜的Fo分离物进行基因组测序，以确定参与致病性的候选基因。这将突出Foa种族之间的差异，但也允许确定特定的诊断目标，以开发基于DNA的病原体快速检测。这些可以被用作生物安全措施，用于检测田间Foa 4爆发或进口芹菜植株或种子中病原体的存在。总体而言，该项目将为培育抗枯萎病的芹菜品种以及Foa 4和其他小种的快速特异性测试提供第一个重要步骤。因此，这些结果将有利于芹菜育种者，生产者和消费者以及植物卫生机构，减轻病原体的生物安全风险。

The Fusarium oxysporum (Fo) fungal species complex includes more than 100 different pathogenic formae speciales (f.spp.) adapted to specific hosts, including important crops such as celery, lettuce, tomato and herbs such as coriander. Fo pathogens continue to spread globally with some responsible for major pandemics, most notably Fo f.sp. cubense causing Panama disease on banana. The impact of Fo pathogens is often substantial with complete crop loss not unusual, and this has been exacerbated by an absence of biosecurity measures and the lack of foresight in developing and deploying plant resistance in advance of new Fo f.spp. and races arriving from other regions. Fo f.sp. apii (Foa) causes Fusarium wilt of celery and is the most important and significant disease affecting production. Infection occurs through the roots and is initiated by long-lived spores in the soil. The plant's vascular system becomes invaded leading to stunting, yellowing and wilting. Control of Foa is very challenging with high losses as fungicides and rotations are ineffective; hence the development of plant resistance is a priority. However, like some other Fo f.spp., new Foa races have evolved which overcome resistance. Four races of Foa exist with the recently emerged race 4 the most damaging in the absence of resistance in commercial celery. Furthermore, unlike other Foa races, Foa4 can also cause disease on coriander. There is therefore an urgent need to develop high level resistance to this disease in celery and assess impact on coriander in the UK. Currently Foa mainly affects celery production in the USA and China but there is a very high risk of the pathogen spreading to major crop and seed production areas in Europe such as Spain, Italy and the UK where conditions are already suitable, but which will become more conducive with climate change. Celery is a major crop worldwide and is an important part of a healthy diet as it is high in fibre, minerals and vitamins. The biggest producers of celery are the USA and Spain but there is also substantial production in the UK. Significantly, UK-based Gs Growers who are the biggest producer of celery in Europe grow a large proportion of their crop in Spain for all year-round supply. The crop is also critical for project partner Tozer Seeds as they are one of the major celery breeders and seed suppliers worldwide. It is therefore very important that celery crops in Europe and the UK are protected against future arrival of Foa4.The main aim of this project is to address the challenge of Fusarium wilt by identifying new sources of resistance to Foa4 in a diverse set of celery types from Tozer Seeds. In addition, we will also assess the response of selected commercial coriander lines to the pathogen. As the genomes of the celery diversity set have just been sequenced, we will also identify parts of the genome and variations in gene sequences associated with this resistance in order to develop DNA markers. These can significantly speed up breeding new varieties as resistance is easily identified by DNA analysis without the need for a plant test. Lastly, we will also carry out genome sequencing of Foa isolates from different races as well as an isolate of Fo from coriander to identify gene candidates involved in pathogenicity. This will highlight differences between Foa races but also allow specific diagnostic targets to be identified for development of rapid DNA-based tests for the pathogen. These could then be employed as a biosecurity measure for detection of Foa4 outbreaks in the field or the presence of the pathogen in imported celery plants or seed.Overall, the project will provide the first important steps for breeding celery cultivars resistant to Fusarium wilt as well as a rapid specific test for Foa4 and other races. These outcomes will therefore benefit celery breeders, producers and consumers as well as plant health agencies by mitigating the biosecurity risk of the pathogen.